This abbreviation is how a famous conductor, Michael Tilson Thomas, is referred to (and I believe he introduced it:)). I heard him conduct many times, and I greatly enjoyed his spark and liveliness, and even his habit of talking between musical pieces.
Last year, MTT returned to conducting after an extremely difficult battle with brain cancer, and on Tuesday, I attended his concert for the first time after his return. He is very frail, and it is very difficult to recognize him. He was helped on the stage. Yet, his performance was spectacular, and the audience gave him a standing ovation. Most importantly, he was visibly happy being in the environment, which has been the essence of his life for a half-century.
Copying from his website (that’s not like he looks now, but I will always remember him this way)

Dear Friends,
My return to performing these last months has been very special. The 20 concerts with the New York Philharmonic, the Los Angeles Philharmonic, and the San Francisco Symphony were heartwarming. Making music with these great artists and for so many friends in the audience felt like coming home, like coming back to life. I couldn’t have been happier.
It takes strength to meet the demands of the music and to collaborate on the highest level with the remarkable musicians who so generously welcomed me. I now see that it is time for me to consider what level of work and responsibilities I can sustain in the future.
I have not publicly discussed my medical diagnosis. I have Glioblastoma Multiforme, a type of aggressive brain cancer. I had an operation to remove what was visible and had radiation and chemotherapy. Currently the cancer is in check. But the future is uncertain as Glioblastoma is a stealthy adversary. Its recurrence is, unfortunately, the rule rather than the exception.
I’m taking stock of my life and will be reducing my administrative responsibilities. I have decided that, after 34 years, I will be stepping down as the Artistic Director of the New World Symphony. This organization, which I co-founded with Lin and Ted Arison, has been and will continue to be a vital and ever-growing resource for musicians. I’m proud of what we have accomplished and very proud of our 1,200 alumni. I will soon assume the role of Artistic Director Laureate and will dedicate myself to working with the NWS Fellows and Alumni on adventurous projects that have long been close to my heart.
I look forward to my work the remainder of this season with orchestras in the United States and Europe and to the many musical collaborations planned for next season. I intend to stick around for a bit. Creating and collaborating to make great music is what it’s all about for me. Every moment on stage with my colleagues is memorable. I want to thank all who have been supportive during this time, especially my husband Joshua Robison. He has always been by my side and is, as ever, my hero.
I will continue to compose, to write, and to mull over your thoughts and mine. I’m planning more time to wonder, wander, cook, and spend time with loved ones – two legged and four. Life is precious.
I send affection and gratitude.
Michael TT